The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Stroke is a manifestation of vascular injury to the brain which is commonly secondary to atherosclerosis or hypertension, and is the third leading cause of death (and the second most common cause of neurologic disability) in the United States. Stroke can be categorized into two broad types, “ischemic stroke” and “hemorrhagic stroke.” Additionally, a patient may experience transient ischemic attacks, which are in turn a high risk factor for the future development of a more severe episode.
Ischemic stroke encompasses thrombotic, embolic, lacunar and hypoperfusion types of strokes. Thrombi are occlusions of arteries created in situ within the brain, while emboli are occlusions caused by material from a distant source, such as the heart and major vessels, often dislodged due to myocardial infarct or atrial fibrillation. Less frequently, thrombi may also result from vascular inflammation due to disorders such as meningitis. Thrombi or emboli can result from atherosclerosis or other disorders, for example, arteritis, and lead to physical obstruction of arterial blood supply to the brain. Lacunar stroke refers to an infarct within non-cortical regions of the brain. Hypoperfusion embodies diffuse injury caused by non-localized cerebral ischemia, typically caused by myocardial infarction and arrhythmia.
The onset of ischemic stroke is often abrupt, and can become an “evolving stroke” manifested by neurologic deficits that worsen over a 24-48 hour period. In evolving stroke, “stroke-associated symptom(s)” commonly include unilateral neurologic dysfunction that extends progressively, without producing headache or fever. Evolving stroke may also become a “completed stroke,” in which symptoms develop rapidly and are maximal within a few minutes.
Hemorrhagic stroke is caused by intracerebral or subarachnoid hemorrhage, i.e., bleeding into brain tissue, following blood vessel rupture within the brain. Intracerebral and subarachnoid hemorrhage are subsets of a broader category of hemorrhage referred to as intracranial hemorrhage. Intracerebral hemorrhage is typically due to chronic hypertension, and a resulting rupture of an arteriosclerotic vessel. Stroke-associated symptom(s) of intracerebral hemorrhage are abrupt, with the onset of headache and steadily increasing neurological deficits. Nausea, vomiting, delirium, seizures and loss of consciousness are additional common stroke-associated symptoms.
In contrast, most subarachnoid hemorrhage is caused by head trauma or aneurysm rupture which is accompanied by high pressure blood release which also causes direct cellular trauma. Prior to rupture, aneurysms may be asymptomatic, or occasionally associated with tension or migraine headaches. However, headache typically becomes acute and severe upon rupture, and may be accompanied by varying degrees of neurological deficit, vomiting, dizziness, and altered pulse and respiratory rates.
Transient ischemic attacks (TIAs) have a sudden onset and brief duration, typically 2-30 minutes. Most TIAs are due to emboli from atherosclerotic plaques, often originating in the arteries of the neck, and can result from brief interruptions of blood flow. The symptoms of TIAs are identical to those of stroke, but are only transient. Concomitant with underlying risk factors, patients experiencing TIAs are at a markedly increased risk for stroke.
The foregoing can be viewed as a manifestation of “brain ischemia.” For example, the long-standing definition of TIAs has been based on the assumption that TIAs are associated with complete resolution of brain ischemia occurring rapidly enough to cause only transient symptoms. In contrast, ischemic stroke was thought to cause permanent injury to brain tissues. The similarity of these acute clinical syndromes made it difficult to differentiate them; they were distinguished on the basis of an arbitrary criterion for the duration of symptoms. But the development of symptoms of acute cerebral ischemia constitutes a medical emergency.
Concepts of brain ischemia and the temporal correlation with clinical events have changed considerably on the basis of studies using computed tomography (CT), magnetic resonance imaging (MRI), positron-emission tomography, and other imaging techniques. However, determining the immediate cause of verebral ischemia and differentiating ischemic from hemorrhagic stroke is difficult. CT scans can detect parenchymal bleeding greater than 1 cm and 95% of all subarachnoid hemorrhages. CT scan often cannot detect ischemic strokes until 6 hours from onset, depending on the infarct size. MRI may be more effective than CT scan in early detection of ischemic stroke, but it is less accurate at differentiating ischemic from hemorrhagic stroke, and is not widely available. An electrocardiogram (ECG) can be used in certain circumstances to identify a cardiac cause of stroke. Angiography is a definitive test to identify stenosis or occlusion of large and small cranial blood vessels, and can locate the cause of subarachnoid hemorrhages, define aneurysms, and detect cerebral vasospasm. It is, however, an invasive procedure that is also limited by cost and availability. Coagulation studies can also be used to rule out a coagulation disorder (coagulopathy) as a cause of hemorrhagic stroke.
Immediate diagnosis and care of a patient experiencing stroke can be critical. For example, tissue plasminogen activator (TPA) given within three hours of symptom onset in ischemic stroke is beneficial for selected acute stroke patients. Alternatively, patients may benefit from anticoagulants (e.g., heparin) if they are not candidates for TPA therapy. In contrast, thrombolytics and anticoagulants are strongly contraindicated in hemorrhagic strokes. Thus, early differentiation of ischemic events from hemorrhagic events is imperative. Moreover, delays in the confirmation of stroke diagnosis and the identification of stroke type limit the number of patients that may benefit from early intervention therapy. Finally, there are currently no diagnostic methods that can identify a TIA, or predict delayed neurological deficits which are often detected at a time after onset concurrent with the presentation of symptoms.
Accordingly, there is a present need in the art for a rapid, sensitive and specific diagnostic assay for stroke and TIA that can also differentiate the stroke type and identify those individuals at risk for delayed neurological deficits. Such a diagnostic assay would greatly increase the number of patients that can receive beneficial stroke treatment and therapy, and reduce the costs associated with incorrect stroke diagnosis.